Options with upgrading?

[rullingen]

Hi there, wondering if anybody can help me out...

I have an
iPhone 3GS
iOS 4.0.1
Jailbroken with jailbreakme.com
Carrier unlocked with Ultrasn0w
Model MC131B

I know upgrading to 4.2.1 is out of the question at the moment due to the carrier unlock but I heard that if I upgrade to 4.1 whilst preserving my baseband then I can still use ultrasn0w.
Is this true? Does someone have a guide? I could only find guides for iP4.

Cheers in advance.

[DevouredDreams]

sn0wbreeze will preserve the baseband but if you wanted to wait till later today when the 4.1 baseband is unlocked you could do a stock firmware upgrade which will be easier

[iYeow]

Yes, you can by restoring to custom firmware created by Pwnage tools 4.1.2 or snowbreeze 2.1